Stronger static types, was Re: [Haskell-cafe] Re: Versioning
brianh at metamilk.com
Thu Dec 21 17:46:10 EST 2006
Jacques Carette wrote:
> Yes, dependent types have a lot to do with all this. And I am an
> eager lurker of all this Epigram.
Would it be possible to augment Haskell's type system so that it was the
same as that used in Epigram?
Epigram itself uses a novel 2d layout and a novel way of writing programs
(by creating a proof interactively) but these seem orthogonal to the actual
type system itself.
Also, typing is not the only issue for compile time guarantees. Consider:
data Dir = Left | Right | Up | Down deriving Eq
-- Compiler can check the function is total
foo :: Dir -> String
foo Left = "Horizontal"
foo Right = "Horizontal"
foo Up = "Vertical"
foo Down = "Vertical"
-- Less verbose but compiler can't look inside guards
foo x | x == Left || x == Right = "Horizontal"
foo x | x == Up || x == Down = "Vertical"
versus something like:
foo (Left || Right) = ...
foo (Up || Down) = ...
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